Altitude and distance recorder



Sept. 2, 1952 M. WALLACE 2,609,532

ALTITUDE AND DISTANCE RECORDER Filed June 16, 1947 V INTERROGATOR l3 RADIO RECEIVER TRANSMITTER JOFF P MULTl-VIBRATOR l4 PULSER /2' l sYNoI-IRoNous METER 2O SIGNAL RECEIVER 6\ AIRBORNE EQUIPMENT SYNCHRONIZING BI FRAMING MECHANISM 22\ TIME DRIVEN CODE KEYER TRANSPONDER so -r REcEIvER GROUND EQUIPMENT 'J J MULTI-VIRRATOR *1 I l SYNGHRONOUS l TRANsMITTER 1 SIGNAL GENERATOR I I Z] wuum lon MARCEL WALLACE pulsed type-Hate (iterates Patented Sept. 2, 1952 UNITED STATES PATENT OFFICE- ALIiT'U DE AND DISTANCE RECORDER Mamet Wanaee, East Port-"Chester,- cunm, as-

said Wallace; doing business as. Panoramic Laboratories, Ea'stPm-t Chester, Conn.

Animation 31111516. 1947, sesame; 754,911

15- Claims.- (C1; Ma -t) 'apiilicatien a communism-impart of applications" for s; Patent #633138, filed thename's; of Wallace" and Wu on December 6-,

iniitfu. he the transmissitns 'ndrmally p-rdvided in QOI n' htiDn with 51817 nee measurin equip- Indistanee easunng equipments which (j-peifatefinitfiebifihbibl hf 'measujrmg travel time ofi suises 6f ere'ctren a netic energy to a reflect inE d i d alil'd. babktd the-sburce Qf nifgiy, the Precise timing. Of the. transmitted purses net normaliy been a matter of importance, since only the elapsed time between transmissions re Qeiitfons has, had si nificance in determini g range 61? di'stamjei In systems Wh'efi'ein a large number at distance measuring equipments bi the en the same frequency and a relatively restne eds ar" a, it in fast been the cdn'ventibii' practice. to. transmit from each, of the equipments at 'ra'neom, tjd 'avdid b1 i imize the possibility are interference between the separate equipments.

'At. the. resent aftype orrdistancemeasurmg, system which has received the. aIJD'rJOVaI 0f the, Civil, Aeronautics Authority, mi determinin the distance 'Qf. aircraft frbm a transponder br tepeater station Iobate'd at "an airport for ether fixed, lo'catiom providesfior the. transmission, friim each of a plurality of aircraft of pulses, at random times anew-1th random spacings, bbth with respect the tran'smis's'idn's from any omen graft and; with respeet tb the'trans'mi'ssioiis fifQin the. varibus aircraft, eb'n'siid'ere'cf as a. jg-rgup. The

' for the random character oi the titansons is, asthereinfiefbr'e has' bjeen indicated, to aireid '01 t0. minimize; the nossibiii'ty of int-en ferenee between measuring equipments aft of which receive signals from the same. transponder. 'i'h'e. receiver oi: each of the distance measurin equipments is gated to enable reception of pulses only (i-luring times after pulse tnans'missibns' which dorrespond 't'o thi3"'1fang'e' which the "e uipment is momentarily measuring; By causing the average time between transmitted pulsesin a given equipment to be large relatively to the time the receiver of that equipment is gatecf'bperr, the

' in the course of time, and accordance which are transmit 2 maj'brity' bi nurse's transmitted; 'adjaieent equipments, are not effective withrresnect ta the given equipment, and those which do' "escape Ipat the time gate, due to their random bceiirrence, have negligible efiect the range measurement.

It is my eonce'ptidn that the times or time. *p'sitime of transmissidn of pulses emitted by the pulse type distance measuring equipment; awe-'- briefly deserib'ed, may he @ntrelledin accordancethe val-tie of a measumbie quahtity; w oht m iestro yine, or, "in faet; a fieeting i m any we the advantages and mode of performance-0f distance measi i ri'ng equipment; The time tibns "of the emitteehpuIse's mm any eesfred number of pulse transmitters-may be transiatett at an iniicati-n'g 'e'r reedrding station, remete from the several pulse transmitters, in terms iii? the Val-t es of the measurable quantity; piotieiing alt the-staitidneihtimioiisi'n'di 'eations, in transient erpei ma-nerit form, of '{the Valiles of'the-q' tion t the transmission of altitude infermaitidn from a piiii'aiity 6f" aireraft, by'mearfs '01 time position Indentation (if the pulses which are transmitted by the era-ftirithe processes-"thiaming distanee'nieasiiremerits. 1 e I In Order to make eeeetive ppfibati'dn bf 212 system of pulse timing modulation meters-mans purposes, a reference time must be preview as well as a refereneetime seaTewhieh are mon tethe entire system, so-th 'at the time tions of pulses transmitted 16y "varibustransmit ters tb represent various tel emetric' values, sh'aH be translatable or interpretable ten-as of is common reference time and time s'eaiet ft is exp'eetedthat substantiallyalfl 'akiriao Will,

the requirements of the Git/ ii Aeronautics Autherit he provided with oiiirfi-ctirectibnali beaeen sits tems, and since such systems provide tra n't-[nits sinus at a fixed- 'fieqflehey' and ataeenstantpmse, I prefer to'atilize these transmissions 'tapi'aviie the requirecf time "scale, as well as-the i eq-uiiz'ed zeros at time. It will" be tinferstood, howeveiz, thatiitilfizatidn of trainsmi ssieii'swli-ieh are any event available; iii-wolves merely a matter of cenvenience; and that "a time seam-me zem time "referenees tor the system of the "iri-ver ititirt may -beprovi'ded etherways; have dismissed herein-before the eahept es impressed time position modirl atibn's on pnisee ted any event tor-the mire pbs'e" 0f making distance measurements. iii-nation of translating er interpreting'the medwa Iated pursesmay be a'c'cempl-ishee by-mean use.

' i distance;

line scanning recorder, of the type now quite common and Well known in connection with facsimile recording, and having a helical platen which scans, by virtue of a rotary motion imparted thereto, laterally of a time-fed record receiving surface, in synchronism with the pulse transmissions, each possible time position of the transmittedpulses bearing adefinite and invariable correspondence With a recording positlon on a line extending laterally across the record receiving surface. 1

Accordingly, it is an object of the" present in vention to provide a telemetric-system of the type utilizing pulsetime'modulation.

It is a further object of the invention to pro vide an improved pulse type distance measuring apparatus, wherein the time positions of pulses otherwise transmitted for the purpose of measuring distance, provide a measure of the value of a .objects;:su.ch as aircraft, by modulating the time positions ofj-pulses otherwise transmittedfrorn theaircraft for purposes of measuring. range or distancewhr c; Q. .7 V I, I I Morezbroadly stated it is an object of the invention toincrease theusefulness of pulse type distance --measuring equipments by assigning s nificance to the timing of the-transmitted pulses. I:

g It is another; object} of the tofprovide ,I mea ns of leads from the coil 9 to a pair of slip rings 1 l "secured to the shaft 8, andthence V to a pair of brushes IZ, leads from which extend I a-H ecord rion recordi t ic val es by I interpretationof the time positions of pulses otherwisetrans nitted for the purpose of measur- ::,;..The above and, still further objects and advantagesg'of the invention will become apparent uponstudy of the following detailed description of a specific embodimentthereof, especially when taken-in conjunction with the accompanying drawings, wherein: I I I Figure 1 is a functio a1 block diagram of an interrogator-responsor, or pulse transmitter and receiver, adapted for measuring distance, and modifiedin accordance with the present invention,and a functional block diagram of a telemetricprecording station, in accordance with the invention; and I I I I I rFi ureI2 is aplan view of a record created in accordance withthe invention. I I I I I Referring now more specifically to the drawings, the reference numeral i. denotes a radio transmitter, which operatesat any convenient and constant frequency, say 150 mc., for purposes of example. The transmitter l is associated with a pulser 2, which serves to energize the transmitter I to transmit short pulses or bursts of radio frequency energy in response to each control pulse applied to the pulser. Control pulses forthe pulser 2 are developed by means o f an equipment of the type disclosed in the aforementioned U. S. Patent, No. 2,505,314, and comprises an altimeter 3 of theaneroid cell. typev which serves; to position an :angularly, positionable pointer 4, about a pivot point 5, causing the pointer 4; to assume an angular position corresponding with and determined by the altitude measured: by; thea met r 3- fi ur to th pointer 4 in any convenient fashion is a small permanent magnet 6. A synchronous motor 1 drives a shaft 8, which is aligned with the pivot point 5, and to whieh'is secured an arm 8a hav- I up coil 9 past the magnet 6 there is induced in I the coil 9 a voltage. This voltage is conveyed by to the pulser;2, and apply to the pulser ,2 for control purposes the voltages induced in the I coil 9.1

The equipment and apparatus described in the preceding two paragraphs may be briefly described as an altitude'timed pulse transmitter,

and will be so referred to hereinafter, since its function is to provide pulses or brief bursts-of radio frequency. energy at times, with respect to an arbitrary time scale. determined, and defined by therotation of the synchronous motor 1,.which' depend 'upon the reading of an aneroid cell altimeter 3 and hence upon altitude. II T I we 'ay assume that a plurality of the altitude timed pulse transmitters hereinbefore described are mounted each in a'fdifie'r'ent aircraft,""and that the synchronous motors I aboard all the air-. craftfare constrained to operate atf'a precisely common frequency, and with a precisely common phase'or framing, by means" which :will be dej scribed indetail hereinafter. Underjsu'oh condi' tions the various aircraft will transmit periodic pulses, all at a common repetition "rate," and all timed with respect to the same arbitrary zer'o'of time and with respect to thesame timejs cale"; but the pulse transmissions from each of the air craft having time positions, or phases, which are determinedjhy the instantaneous altitude -off'the There has been discussed hereinbefore quite briefly the theory of operation of the pulse trans-f mission typefofdistance measuring equipment; wherein pulses are transmitted at randomfrom a transmitteraboard each 'of a plurality oi?v air craft, "and are repeated from a common transponder T located at a ground stationfus'ually at a significantjlocati'on such. .as an airport'or an aircraft carrier, and wherein the time required for transmission of the pulses to the transponder and back toa receiver associated with the transmitter is measured to determine range; It has been explained that the random character of the transmitted pulses is enforced for the purpose of minimizinginterferences between aircraft which I V IL More specifically I propose to utilize theftrans init't'er V asthev interrogatorof a pulse type of distance measuring equipmentfwhich is in es.- sence merely an 'interrogato'r-responsor; Thereby each aircraft is constrained to transmit pulses at the same repetition rate, but at time positions corresponding withaltitude, so that aircraft fly ing at I even slightly distinct and different altisi ons. An ordered randomness is introduced into the transmissions ofthe interrogators: of the distance measuring equipments which serves to prevent interference-between transmissions from distinct aircraft with the same efiective'ness as has been the case-hitherto by chance random.

The'eontrol of pulse tiniing in tleinterro'gators or "the present system in accordance with the value ofa variable parameter, forexamplealtitude, enables determination at remote stations of the values of said parameter as associated with each of the transmitting aircraft, and in accordance with the principles and apparatus disclosed in S. Patent $1 2,534,939, referred to supra, the valuesef said tparameterimay also the recorded in permanent form on a time fed and time calibrated record receivingsurfabe oristrip.

Bisregarding :for the immediate present the distancemea'suring functions of the airborne equipment of thepresent system,.and'turning'our attention to the ground recording station, there is provided'apulse receiver'sibarranged 'toreceive and :demodulate pulse signals of the character of those transmittedby the airborne transmitters or interrogators of the system. Detected pulses provided by the receiver are applied, after amplificationif required, to the marker elec.-;

fimdfi 3"! 9f a (facsimile type recorder 32, having a helical platen 33 and a timefedre'cord receiving'surface'flr The specific character and 51313110: ture orgthe recorder 32 forms no part of the presentinv nt on. and may utilize various re,- corders cf the indicated, such recorders bein a a abl purch se comme ci l y a having been thesubject of the grant of a considerable number of Letters Patent of the United States, I specify, howevgr, that a recorder of th y 'q e d n U S iat t $06 issued to Q. J, Youngand dated September 24, 19 0 s efiisfa er t he u po in ha n 1? r ier nce t9 that Ba entie a ful an complete disclosure of a -suitable recording mechan eef it o sta e he r sent ap l c tion, that marks are created on thaj surface 34 9 1? a pli ion 0 th ma ker 3 of a i c n voltage} the lateral position of the mark beingdetermmed by the instantaneous position of the helical platen at the instant of application of the said voltage. The platen- 33 ofthe recorder 311 at b ns-9 a sin hren u m t 75 at thesarnespeed and with the same framing Ph se as a e t a i sy ch en us eter located at the telemetric transmitters of the syse t m nd, w h cause r ien of ul e e era n r cke ce In Qrder he assu h t chronous motor'35 and the various synchronous motors 5 shall be synchronized and identically tra ned, the motor 35 is utilized to controla syn-e dhronizinglsignal generator 36, which supplies its Output to a radio transmitter 31 tuned-to transe mi t, on the frequency to which are tuned synchroniaing signal receivers '20, located at the telemetric transmitting stations of the system. The specific structure and mode of operation "of the sync a g n at ng equipment i d at the receiving and recording station of the present system forms no part of the invention, it being sufficient that signals be"provid ed which are of suitable character to cooperate with the synchronizing and framingequipment at the various telemetric transmitters, to assure that the motors I will maintain precise framing and synchronizationiwith respect to the metor'35. Many transmission at such synchronizing and draining: systems: area available in the pri'cr art,andn fdo'lnotidesire to be-' restricted to any-particular one or such;

systems. I-have, however, specified one specific. system whichiprefer to employ, aful'ldescripe: tion ofwhich, both in respect tostructuretrand. mode of operation, is to be round in LettersPan ent of the United States, No. 2, 263 '64-1-,sto Nicole son. 2

A further signal whieh maybe utilizedi'forisynei chronizingthe present system, as-has been; briefly indicated hereinbefore, is the 'orrmi direic, tional beacon system of the type appreve'd by the Civil Aeronautics Authority".for instailaition generally at airports- This systemoperates by transmitting a rotating pattern-of energy and a fixed pattern {of omnidirectional energy, the speed of rotation of the rotating pattern being related in frequency to a modulation -ircq11enc3' or 30 cycles er second; impressed. "on the enamdirec'ticnal transmissien; The so cyele si'gnal provides a convenient-synchronizing signal and may be employed to drive all the synchronous: motors I and 350i thepr'esentsystem at identical speeds, suitable framing signals maylbe superconjunction with the presentsystem, asabo'veindicated, I do not consider "the use of 'any spe cific'such' system to be essential, and the various systems suggested are mtended tor purposes at exemplification only. l i By'virtue ofthe' identical framing and rotative speed of the recorder motor 35 an ler "the telemetric transmitter motors 1, a common z'erot ot time may be provided ffor an the-equipments of the present system, and thecoil supporting arms 8a as well asthe helical platen 3t 'may 'so la'e arranged that upon passage of the coilsfiBa aid-- jacent" -'ameter position corresponding with zero value of the measured quantity, or of zero an'gfu Iar displacementofthe meter pointer 4, the helical platen 33 shall be so phasedas to'be poten tially able to create a mark on the record're ceiving surface ata point correspondingwith a zero calibration line antecedently provided fen the surface. 'The record receiving surface may be calibrated "laterally, by means of laterally spaced, parallel lines 3}), provided thereon gsee Figure 2) to enable determination of the valuepi any mark created on the paper. The total lateral dimension of the record receiving suriace 34, or any predetermined portion thereof, may be caused to correspond with the total possible'ang-ular displacementof-the pointer 4 or the ane'roid cell and the total altitude range ofthesys tem.

It will 'be recalled that the transmitter [performs its primary function as an interrogator of an interrogator-respensor or distance measuring equipment. The respon's'or of the distance measuring eq ipment comprises a receiver {3 which is normallyinoperative, but which is keyed thereto, at which time it returns to its original-- The time between successive pulses is "chosen 7 tobelarge in relation to the time of propagation of electromagnetic energy for the maximum intended rangeof the equipment, by a'factor of theorderof 100 to 1009, so that there is inefiect a time sharing as between various aircraft of thesystem for range measuring purposes.

-,=;-Range at any one aircraft may be measured in I terms oflthe total operating time of the multi-- vibrator 'l 4, which in turn determines the average Qf. certain currents or voltages of the multivibratoryin a manner which is well known per se, these currents or voltages-being measurable by means of a voltmeter or ammeter l to determine. range or distance.

i The specific character of the distance measuring equipmentntilized in my invention isper se-well known, and is subject to modification in detail, in any event, and it is accordingly deemed unnecessary to" complicate the description and illustration of the system with a full and complete circuit diagram and exposition thereof. I

have: accordingly disclosed and described same onlyto the entent required to enable those skilled in the art to understand the principles and mode of operation of myinvention.

Since the various transmitted altitudeirepre sentative signals of: the present invention are indistinguishable, except in respect to magnitude, I have provided in circuit withthe pulser 2, and between the pulser 2 and thhe pick-up coil 9, a time driven code keyer 22, which interrupts transmissions from each of the transmitters of L the system at relatively long intervals, and in a coded sequence. By interrupting the control impulses applied to the pulser 2, transmissions from the transmitter l. are likewise interrupted,

asarethereby the altitude'records at the ground station, .By examining the coded interruptions of the records at the ground station each altitude record may be identified in terms of'itsoriginating aircraft.

. Reference is made to Fiigure 2 of the drawings for, an illustration .of the appearance ofa record as provided bythe apparatus of the invention. The arrow labelled time represents the longi; tudinal direction of feed of recordreceiving surface 34 with time, the lines 25 audit representing time records of aircraft altitude, and each of the records being interrupted at intervals; in a; coded sequence 21, to identify the record, or to relate same with a specific aircraft.

-It will be realized that the transmitting equipments built in accordance with the present invention transmit atmospheric pressure, rather than timealtitude, so'that fora given time altitude transmissions.fromtheivarious aircraft of the, systemmay vary from day today or-ifrom hour to hour, in accordance with the value of ambient pressure temporarily existing in. a given area. To overcome this difficulty, the calibrations provided on the record receiving surface 34 may DQJDE'QVidBd under control of the value of local altitudeexistingon theg i ound; There is thereby; provided an automatic correction for variationsin local atmospheric pressure, since the valueof;

each altituderecord-maybe referred to a corrected calibration mark. Specifically, I provide at the ground station an altitude timed pulse generator 28, similar to that provided on the" various aircraft of the system, for generating a control pulse timed, with respect to the arbitrary zero of time of-the system, to correspondwith sea level altitude for standard conditions of .atmosphe p essu 'li ep l rator 28 s n:

chronizes a multiplying;oscillator of the multi vibrator type 2 9, which provides a number of out-;

put pulses, equallyspaced, for each control pulse inserted therein;- The pulses providedby the multi-vibrator are so spacedthat; when'applied to the recorder 32, properly spaced calibration lines are recorded on'the record receiving sure, face 34, the pulse frequency. of the multi-vibrator 29 being fixedandthe pulse separationbeing properly chosen for that purpose. The phasing or time positioning of the pulses are determined,"

however, bythe pulse timing of the output of the control pulses 28, the latter being determinedirt partjby local atmospheric conditions, the calibration lines varying in lateral position. on the surface .34,:all simultaneously, in accordance with such conditions. Examples of suitable calibration lines are provided in -l*"igure i, variations from linearity of thelines 35 being occasioned by'variations of atmospheric pressure; and: the position of the lines with respect to the edges of the sur face 34 being of significance primarily'indetermining the existence 0f such variations.

In accordance withthesystem of the' present invention, all the aircraft as well as the ground station, may-utilize aneroid altimeters pre-calibrated for standard atmospheric conditions, and proper and correct readings of altitude will 'be" provided at various recording stations, or at the same recording station at various times, without introducing altitude corrections into the altime ter or the various aircraft.

While I have described one embodiment of my invention, it will be clear that variations and modifications thereof maybe resorted to without departing from the true spiritfand'scope' of 'the invention as defined in the appended claims What I claim and desire to secure byLetters Patent of the United States is:' f: '1. In an airborne distance measuring equip ment, a pulse transmitter, a pulse receiver having means for increasing and decreasing the gain thereof, means responsive to the transmissionof'a" pulse by saidtransmitte'r for increasing the gain of said receiver, means responsive to reception of a pulse by said receiver for decreasing the gain of said receiveryand means responsive to the" altitude of said transmitter for determining the time of pulse transmission with respect to an arbitrary zero of time. .1 2 The combination in accordance with claim l" and further comprising a remote indicating means, and means responsive to said transmitted pulses at said remote indicatingmeans for mat. eating the;altitude of saidtransmitterr 3. The combination in accordance with claim 2 wherein said remote indicator comprisesa line scanning recorder for recording the times of 01.5 currence of said transmitted pulses with respect to said arbitrary zero of time. r V

4. In combination, a distance measuring equip-i ment comprising a pulse transmitterrand a' pulse:

I provided by said pulse generatoicomprising a device for measuring the value of a measurable quantity, said last mentioned device comprising a measuring instrument having, a movable pointer, said means for controlling comprising apparatus for scanning the locus of possible positions .of said pointer and for generating a control sig nal upon concurrence of saidxp'cinter position and f, said;scanning apparatus.

5. Thecombination in accordance withclaim 4 andfurther comprising a remote line 'scanning recorder; and means for synchronizing the scan-.

ning actions of, said recorder and of saidappaiatus, said recorder comprising marking means responsive to pulses, transmitted by said pulse transmitter for creating a mark."

6. vIn combination, a, distance measuring device located on an aircraft and comprising a pulse transmitter and a pulse receiver, means for timing the transmitted pulses with respect to. arbitraryzeros of time in accordance with local atmosphericpressure as measured at said aircraft, a remotely located line scanning recorder having a line scanning marker responsive tqelectrical signals and a time-fed record receiving surface, means for receiving said transmitted pulses and for applying electrical signals to said marker in response thereto, means for initiating each scanning action of said marker at one of said arbitrary zeros of time and for extending the scanning action over time periods less than the maximum range of times between said transmitted pulses, and means responsive to local atmospheric pressure at said recorder for applying calibration signals to said line scanning marker at times corresponding with predetermined altitude values.

7. A distance measuring system comprising a plurality of pulse transmitters each aboard a different aircraft, a plurality of pulse receivers each operatively associated with one of said transmitters, a single pulse repeater responsive to all of said pulse transmitters for repeating pulse signals to said pulse receivers, a source of omni-directionally transmitted synchronizing signals, means for measuring altitude aboard said aircraft, and means for controlling the timing of the transmitted pulses from each of said pulse transmitters, within periodic time intervals defined by said synchronizing signals and common to all of said pulse transmitters, in accordance with altitudes of the transmitters as measured by said means for measuring.

8. A distance measuring system, comprising, a pulse transmitter aboard an aircraft, a pulse receiver aboard said aircraft, means for repeating to said receiver, from a remote location, pulses originating in said transmitter, after a time interval representative-of distance of said aircraft from said remote location, means aboard said aircraft for measuring its altitude, and means for predetermining times of pulse transmission from said transmitter in accordance with only the altitude of said aircraft as measured by said means for measuring.

9. A distance measuring system comprising a plurality of pulse transmitters each aboard a different aircraft, a plurality of pulse receivers each operatively associated with one of said plurality of pulse transmitters, means for repeating pulses transmitted from said pulse transmitters from a single ground location to said pulse receivers, means comprising an 0mm-d1- rectional transmitter for delimiting substantial- 1y simultaneously aboard all said aircraft successive periodic time intervals common to said plurality of pulse transmitters, means aboard eachof said aircraft for measuring its altitude,

and means-for displacing the times of transmission of said pulsetransmittedfrom each of said pulse transmitters within said periodic time intervals in response to the means for measuring altitude, and in accordance with the altitude of the transmitter.

10. The combination in accordance with claim 9 wherein is further provided a remote indicator comprising means for indicating the timesof occurrence of said transmitted pulses with res e a d er im nterva t-hs ebrto indicate the altitudes of said plurality-"of aircraft.

- I, 11, The combination in accordance with claim 9 wherein is furtherprovideda remote recerder of the line scanning type, said recorder having meansfor scanning successive lines insynchronism with said successivetime intervals, ,sfaidremote recorder comprising means for creati record in response to eachof said transmitted pulses, thereby to provide aeontinuousnecondof altitudes of saidplurality of aircraft.

12. A distance measuring system, comprising, a plurality of pulse transmitters each aboard an aircraft, a pulse receiver aboard each of said aircraft, means for measuring the magnitude of a measurable quantity aboard each of said aircraft, means for delimiting periodic time intervals aboard all said aircraft which are common to all said aircraft, means aboard each of said aircraft responsive to the means for measuring aboard that aircraft for timing pulses trans mitted by the pulse transmitter aboard that aircraft within said periodic time intervals in accordancewith the magnitude of said quantity, a common pulse repeater for repeating pulses transmitted by all said aircraft to said pulse receivers, means for conditioning each of said receivers to receive substantially only pulses occurring substantially within a time interval after transmission corresponding with the range of the receiver from saidcommon pulse repeater, and means for measuring said time interval aboard each of said aircraft as a measure of the range of said aircraft from said repeater.

13. A distance measuring system, wherein a plurality of distance measuring equipments each comprises a pulse transmitter and a receiver of repeated pulses, wherein a single pulse repeater is provided for repeating pulses transmitted from all said transmitters to all said receivers, and wherein each of said receivers is gated to receive pulses substantially only at times within its own range from said pulse repeater, comprising, separate means coupled to each of said distance measuring equipments for measuring the magnitude of a predetermined quantity, and

means responsive to each of said means for controlling the times of transmission of pulses, from the distance measuring equipment to which it is coupled, within the time interval common to all said distance measuring equipments.

14. In combination, a distance measuring device located on an aircraft and comprising a pulse transmitter and a pulse'receiver, means for timing the transmitted pulses with respect to arbitrary zeros of time in accordance with altitude as measured at said aircraft, a remotely located line scanning recorder having a line scanning marker responsive to electrical signals "and a time fed record receiving suriace, means for receiving said transmitted pulses and for applying electrical signals to said marker in response thereto, means for initiating each scanning action of said marker at one of 'said'arbitrary zeros of time and for extending thescanning action over time periods less than the maximum range of times between said transmitted pulses.

15. In combination, a distance measuring device located on an aircraft and comprising a pulse transmitter and a pulse receiver, means fortiming the pulses transmitted by said pulse transmitter with respect to arbitrary zeros of time in accordance with altitude as measured at'said aircraft, "a remotely located line scanning indicator having a, line scanning marker responsive to electrical signals and a markreceiving suriace responsiveto said marker, means for receiving said transmitted pulses and for applying electrical signals to said marker in response thereto, means for initiating each scanning action of 'said marker at one of said arbitrary zeros of I2 REFERENCES orrEn The following references are of record the v file of this patent:

UNITED STATES PATENTS Number Name Date Luck Aug. 12, 1941 Potter Mar. 21, 1944 Korn July 9; 1946 Smith July 9,1946 Wolflf July 9, 1946 Seeley Aug. 6, 1946 Labin Sept. 10, 1946 Alford Apr. 29,1947 Wight et a1. May '27, 1947 Eaton June 17, 1947 Epstein Nov. 4, 1947 Deloraine Apr. 26,- 1949 McIlwain Sept.27, 1949 Herbst Dec. 6, 1949 Smith 1 Dec. 20, 1949 Benfer Mar.-7, 1950 Krauth Mar. 14, 1950 Busignies July '4, 1950 Busignies Aug. 8, 1950 Deloraine et a1. Sept. 12', 

